A nonlinear partially-averaged Navier–Stokes model with near-wall correction for separated turbulent flow

2021 ◽  
pp. 2150262
Author(s):  
Benqing Liu ◽  
Wei Yang ◽  
Sien Li ◽  
Xianbei Huang
Keyword(s):  
Turbulent Flow ◽  
Wall Friction ◽  
Navier Stokes ◽  
Wall Region ◽  
Good Resolution ◽  
Production Term ◽  
New Model ◽  
Standard Formula ◽  
Turbulent Statistics ◽  
Near Wall

A nonlinear Partially-Averaged Navier–Stokes model with near-wall correction is developed for separated turbulent flow simulations. The periodic hills flow is simulated to validate the new model and the results are compared with the standard [Formula: see text] model, MPANS model, MSST PNAS model, standard [Formula: see text] PANS model, and experimental/LES results. It is found that the new model shows better performance in the prediction of both mean velocity and turbulent statistics compared to the other models. From the prediction of the near-wall friction coefficient of periodic hills flow, the new model shows good resolution in the near-wall region by considering the near-wall damping function to turbulent viscosity, gradient production term, and turbulence scale correction term for the near-wall region. From the analysis of anisotropy-invariant and sub-filtered stress (SFS), it can be found that the nonlinear term is necessary for prediction accuracy improvement in turbulent flow simulation with strong separation.

Large-eddy simulations of tip leakage and secondary flows in an axial compressor cascade using a near-wall turbulence model

2009 ◽  
Vol 223 (6) ◽  
pp. 645-655 ◽  
Author(s):  
D Borello ◽  
G Delibra ◽  
K Hanjalić ◽  
F Rispoli
Keyword(s):  
Secondary Flows ◽  
Tip Clearance ◽  
Navier Stokes ◽  
Wall Region ◽  
Compressor Cascade ◽  
Tip Leakage ◽  
Computational Mesh ◽  
Large Eddy ◽  
Reynolds Averaged Navier Stokes ◽  
Near Wall

This paper reports on the application of unsteady Reynolds averaged Navier—Stokes (U-RANS) and hybrid large-eddy simulation (LES)/Reynolds averaged Navier—Stokes (RANS) methods to predict flows in compressor cascades using an affordable computational mesh. Both approaches use the ζ— f elliptic relaxation eddy-viscosity model, which for U-RANS prevails throughout the flow, whereas for the hybrid the U-RANS is active only in the near-wall region, coupled with the dynamic LES in the rest of the flow. In this ‘seamless’ coupling the dissipation rate in the k-equation is multiplied by a grid-detection function in terms of the ratio of the RANS and LES length scales. The potential of both approaches was tested in several benchmark flows showing satisfactory agreement with the available experimental results. The flow pattern through the tip clearance in a low-speed linear cascade shows close similarity with experimental evidence, indicating that both approaches can reproduce qualitatively the tip leakage and tip separation vortices with a relatively coarse computational mesh. The hybrid method, however, showed to be superior in capturing the evolution of vortical structures and related unsteadiness in the hub and wake regions.

Merging Near-Wall RANS Models With LES for Separating and Reattaching Flows

2006 ◽  
Author(s):  
Suad Jakirlic´ ◽  
Bjo¨rn Kniesner ◽  
Sanjin Sˇaric´ ◽  
Kemal Hanjalic´
Keyword(s):  
Reynolds Number ◽  
Equation Model ◽  
Navier Stokes ◽  
Model Parameters ◽  
Wall Region ◽  
Detached Eddy Simulation ◽  
Rans Model ◽  
Eddy Simulation ◽  
Moderate Reynolds Number ◽  
Near Wall

A method of coupling a low-Reynolds-number k–ε RANS (Reynolds-Averaged Navier-Stokes) model with Large-Eddy Simulation (LES) in a two-layer Hybrid LES/RANS (HLR) scheme is proposed in the present work. The RANS model covers the near-wall region and the LES model the remainder of the flow domain. Two different subgrid-scale (SGS) models in LES were considered, the Smagorinsky model and the one-equation model for the residual kinetic energy (Yoshizawa and Horiuti, 1985), combined with two versions of the RANS ε equation, one governing the “isotropic” (ε˜; Chien, 1982) and the other the “homogeneous” dissipation rate (εh; Jakirlic and Hanjalic, 2002). Both fixed and self-adjusting interface locations were considered. The exchange of the variables across the interface was adjusted by smoothing the turbulence viscosity either by adjusting the RANS model parameters, such as Cμ (Temmerman et al., 2005), or by applying an additional forcing at the interface using a method of digital-filter-based generation of inflow data for spatially developing DNS and LES due to Klein et al. (2003). The feasibility of the method was illustrated against the available DNS, fine- and coarse grid LES, DES (Detached Eddy Simulation) and experiments in turbulent flow over a backward-facing step at a low (Yoshioka et al., 2001) and a high Re number (Vogel and Eaton, 1985), periodic flow over a series of 2-D hills (Fro¨hlich et al., 2005) and in a high-Re flow over a 2-D, wall-mounted hump (Greenblat et al, 2004). Prior to these computations, the method was validated in a fully-developed channel flow at a moderate Reynolds number Rem ≈ 24000 (Abe et al., 2004).

scholarly journals Effect of reverse flow on the pattern of wall shear stress near arterial branches

2011 ◽  
Vol 8 (64) ◽  
pp. 1594-1603 ◽  
Author(s):  
A. Kazakidi ◽  
A. M. Plata ◽  
S. J. Sherwin ◽  
P. D. Weinberg
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Steady Flow ◽  
Stokes Equations ◽  
Reverse Flow ◽  
Side Branch ◽  
Navier Stokes ◽  
Wall Region ◽  
Wall Shear ◽  
Near Wall

Atherosclerotic lesions have a patchy distribution within arteries that suggests a controlling influence of haemodynamic stresses on their development. The distribution near aortic branches varies with age and species, perhaps reflecting differences in these stresses. Our previous work, which assumed steady flow, revealed a dependence of wall shear stress (WSS) patterns on Reynolds number and side-branch flow rate. Here, we examine effects of pulsatile flow. Flow and WSS patterns were computed by applying high-order unstructured spectral/hp element methods to the Newtonian incompressible Navier–Stokes equations in a geometrically simplified model of an aorto-intercostal junction. The effect of pulsatile but non-reversing side-branch flow was small; the aortic WSS pattern resembled that obtained under steady flow conditions, with high WSS upstream and downstream of the branch. When flow in the side branch or in the aortic near-wall region reversed during part of the cycle, significantly different instantaneous patterns were generated, with low WSS appearing upstream and downstream. Time-averaged WSS was similar to the steady flow case, reflecting the short duration of these events, but patterns of the oscillatory shear index for reversing aortic near-wall flow were profoundly altered. Effects of reverse flow may help explain the different distributions of lesions.

Pipe-Wall Friction in Vertical Sand-Slurry Flows

2005 ◽  
Author(s):  
Vaclav Matousek
Keyword(s):  
Lift Force ◽  
Pipe Wall ◽  
Fine Sand ◽  
Coarse Sand ◽  
Solid Particles ◽  
Wall Friction ◽  
Wall Region ◽  
Pressure Drops ◽  
Frictional Pressure Drop ◽  
Near Wall

Friction due to the presence of solid particles suspended in a flow is a result of processes in a relatively thin layer near the pipe wall. Pipe-wall friction generated by particles in permanent contact with pipe wall is relatively well understood. However, very little is known about the friction deriving from sporadic contact (collisions) of particles with the wall. This friction is a major contributor to the frictional pressure drop in many slurry pipeline applications. The paper describes results of extensive laboratory tests of vertical flows of different sand fractions (fine, medium and coarse sands) carried out in the Laboratory of Dredging Engineering of the Delft University. In order to identify mechanisms that govern the solid-particle friction at the pipe wall the paper analyses friction conditions in observed vertical flows. The effects of particle-particle interactions and particle-liquid interactions on the pipe-wall friction are evaluated. One of the interesting phenomena observed in the laboratory was that frictional pressure drops in highly-concentrated flows at high velocities are lower for slurries of medium sand and coarse sand than for slurries of fine sand. The observed trend is believed to be associated with the liquid–lift force acting on solid particles traveling near a pipe wall. This off-wall force seems to be the most effective for medium to coarse particles traveling in highly concentrated mixture in the near-wall region. Thus pressure drops due to the presence of solids in non-stratified flows seem to be primarily produced by the combined effect of the Bagnold collisional force (force that colliding particles exert against the pipe wall) and liquid lift force acting on solid particles in the near-wall zone of the slurry flow.

A Priori Analysis of Explicit Algebraic Stress Models for a Turbulent Flow Through a Straight Square Duct

2004 ◽  
Author(s):  
H. Naji ◽  
O. El Yahyaoui ◽  
G. Mompean
Keyword(s):  
Turbulent Flow ◽  
Reynolds Stress ◽  
Stokes Equations ◽  
A Priori ◽  
Proximity Effects ◽  
Navier Stokes ◽  
Wall Region ◽  
Square Duct ◽  
Anisotropy Tensor ◽  
Stress Models

The ability of two explicit algebraic Reynolds stress models (EARSMs) to accurately predict the problem of fully turbulent flow in a straight square duct is studied. The first model is devised by Gatski and Rumsey (2001) and the second is the one derived by Wallin and Johansson (2000). These models are studied using a priori procedure based on data resulting from direct numerical simulation (DNS) of the Navier-Stokes equations, which is available for this problem. For this case, we show that the equilibrium assumption for the anisotropy tensor is found to be correct. The analysis leans on the maps of the second and third invariants of the Reynolds stress tensor. In order to handle wall-proximity effects in the near-wall region, damping functions are implemented in the two models. The predictions and DNS obtained for a Reynolds number of 4800 both agree well and show that these models are able to predict such flows.

Modelling of hydrogen-air supersonic mixing and combustion in near-wall region

2021 ◽  
Vol 36 (2) ◽  
pp. 101-115
Author(s):  
Roman S. Solomatin ◽  
Ilya V. Semenov
Keyword(s):  
Turbulence Model ◽  
Stokes Equations ◽  
Air Flow ◽  
Flame Stabilization ◽  
Navier Stokes ◽  
Wall Region ◽  
Navier Stokes Equations ◽  
Supersonic Mixing ◽  
Ignition And Combustion ◽  
Near Wall

Abstract Turbulent mixing, ignition, and flame stabilization in the non-premixed supersonic hydrogen-air flow is numerically modelled in a near-wall region. Mixing algorithm based on the turbulence approach SARANS (Reynolds Averaged Navier–Stokes equations closed with Spalart–Allmaras turbulence model) with a diffusion model and a detailed kinetic model for hydrogen-air chemical reactions are employed. The system of governing equations that consists of basic conservation laws and the turbulence model equation is solved in a coupled manner with the LU–SGS–GMRES method. The model is applied to simulate the process of hydrogen injection into a M = 2.44 air flow with their subsequent mixing, ignition, and combustion in the Burrows– Kurkov chamber. The results are compared to available experimental and reference computational data. All calculations are carried out on the ‘MVS-10P’ JSCC RAS supercomputer cluster.

Numerical simulation of turbulent flow in a pipe oscillating around its axis

2000 ◽  
Vol 424 ◽  
pp. 217-241 ◽  
Author(s):  
MAURIZIO QUADRIO ◽  
STEFANO SIBILLA
Keyword(s):  
Turbulent Flow ◽  
Stokes Equations ◽  
Streamwise Vortex ◽  
Longitudinal Axis ◽  
Navier Stokes ◽  
Planar Geometry ◽  
Wall Region ◽  
Navier Stokes Equations ◽  
Moving Wall ◽  
Direct Numerical Solution

The turbulent flow in a cylindrical pipe oscillating around its longitudinal axis is studied via direct numerical solution of the Navier–Stokes equations, and compared to the reference turbulent flow in a fixed pipe and in a pipe with steady rotation. The maximum amount of drag reduction achievable with appropriate oscillations of the pipe wall is found to be of the order of 40%, hence comparable to that of similar flows in planar geometry. The transverse shear layer due to the oscillations induces substantial modifications to the turbulence statistics in the near-wall region, indicating a strong effect on the vortical structures. These modifications are illustrated, together with the implications for the drag-reducing mechanism. A conceptual model of the interaction between the moving wall and a streamwise vortex is discussed.

scholarly journals Large eddy simulation of near-wall turbulent flow over streamlined riblet-structured surface for drag reduction in a rectangular channel

2020 ◽  
Vol 24 (5 Part A) ◽  
pp. 2793-2808
Author(s):  
Hussain Al-Kayiem ◽  
Desmond Lim ◽  
Jundika Kurnia
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Flow ◽  
Drag Reduction ◽  
Rectangular Channel ◽  
Wall Region ◽  
Mean Velocity ◽  
Structured Surface ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Near Wall

Sharkskin-inspired riblets are widely adopted as a passive method for drag reduc?tion of flow over surfaces. In this research, large eddy simulation of turbulent flow over riblet-structured surface in a rectangular channel domain were performed at various Reynolds numbers, ranging from 4200-10000, to probe the resultant drag change, compared to smooth surface. The changes of mean streamwise velocity gradient in wall-normal direction at varied locations around riblet structures were also investigated to reduce mechanisms of streamlined riblet in reducing drag. The computational model is validated by comparing the simulation results against analytical and experimental data, for both smooth and riblet surfaces. Results in?dicating that the performance of the proposed streamlined riblet shows 7% drag reduction, as maximum, which is higher than the performance of L-shaped riblet with higher wetted surface area. The mean velocity profile analysis indicates that the streamlined riblet structures help to reduce longitudinal averaged velocity component rate in the normal to surface direction of near-wall region which leads to laminarization process as fluid-flows over riblet structures.

Study of unsteady cavitating flow around Clark-Y hydrofoil using nonlinear PANS model with near-wall correction

2021 ◽  
Author(s):  
Benqing Liu ◽  
Wei Yang ◽  
Sien Li ◽  
Jie Chen ◽  
Biao Huang ◽  
...  
Keyword(s):  
Turbulent Transport ◽  
Cavitating Flow ◽  
Navier Stokes ◽  
Cloud Cavitation ◽  
Production Term ◽  
Dissipation Term ◽  
Lift And Drag ◽  
Lift And Drag Coefficient ◽  
Drag Ratio ◽  
Near Wall

In this paper, we describe the use of a new nonlinear partially-averaged Navier–Stokes (PANS) model with near-wall correction for simulating the cavitating flow around a Clark-Y hydrofoil. For comparison, the standard [Formula: see text]–[Formula: see text] PANS model is also used. The results demonstrate that compared to [Formula: see text]–[Formula: see text] PANS and experiment, the new PANS model shows better performance for cavitation flow, including time-averaged velocity, root mean square (rms) velocity and cavity shedding processing. Through the calculation of the lift and drag coefficient at [Formula: see text] and [Formula: see text], it can be concluded that the cavitation will decrease the lift and increase the drag of the hydrofoil, resulting in a decrease of the lift-to-drag ratio. From the analysis of different terms in both the turbulent kinetic energy (TKE) and dissipation rate transport equations of the cloud cavitation, it is found that the production term and the dissipation term are dominant in the turbulent transport, and they are mainly distributed in the vapor–liquid interface and the trailing edge of the hydrofoil.

Direct numerical simulation of turbulent flow and heat transfer in a spatially developing turbulent boundary layer laden with particles

2018 ◽  
Vol 845 ◽  
pp. 417-461 ◽  
Author(s):  
Dong Li ◽  
Kun Luo ◽  
Jianren Fan
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Turbulent Flow ◽  
Solid Particles ◽  
Heated Wall ◽  
Wall Region ◽  
Flow And Heat Transfer ◽  
Particle Laden Flows ◽  
Near Wall

Direct numerical simulations of particle-laden flows in a spatially developing turbulent thermal boundary layer over an isothermally heated wall have been performed with realistic fully developed turbulent inflow boundary conditions. To the authors’ best knowledge, this is the first time the effects of inertial solid particles on turbulent flow and heat transfer in a flat-plate turbulent boundary layer have been investigated, using a two-way coupled Eulerian–Lagrangian method. Results indicate that the presence of particles increases the mean streamwise velocity and temperature gradients of the fluid in the near-wall region. As a result, the skin-friction drag and heat transfer are significantly enhanced in the particle-laden flows with respect to the single-phase flow. The near-wall sweep and ejection motions are suppressed by the particles and hence the Reynolds shear stress and wall-normal turbulent heat flux are attenuated, which leads to reductions in the production of the turbulent kinetic energy and temperature fluctuations. In addition, the coherence and spacing of the near-wall velocity and temperature streaky structures are distinctly increased, while the turbulent vortical structures appear to be disorganized under the effect of the particles. Moreover, the intensity of the streamwise vortices decreases monotonically with increasing particle inertia.

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